1. Field of the Invention
The present invention relates to a control system for a clothes dryer. In particular, a moisture sensor is provided to terminate a drying process when the amount of moisture present in the clothes inside the dryer reaches a desired level as selected by a user. Additionally, the clothes dryer of this invention includes a drying schedule which estimates the amount of drying time left in the current cycle, by taking into account differences between an initial estimation and the final result each time the dryer has been run. The length of a cooldown sequence is also updated.
2. Discussion of the Prior Art
It is well known in the art to provide a clothes dryer with a simple time-dry control, in addition to a sensor-dry mode. When the time-dry control is used, the user places the wet articles inside the dryer and selects a duration for the drying process. Because there is little or no automatic control or adjustment during the process, the drying process simply continues until the time expires. The result can be inefficient, because it is difficult for a user to accurately estimate the time required to reach a desired, final moisture level prior to operating the machine.
In comparison, sensor-dry modes are provided to automatically control a drying operation. Specifically, when a sensor-dry mode is selected, the user places wet articles inside the dryer drum and selects a final dryness level. Instead of forcing the user to guess how long the process should take, the machine stops when the desired dryness level is reached. For this purpose, the machine includes at least one sensor for detecting the level of moisture of the articles. The machine simply operates until the moisture sensor detects the final desired dryness level selected by the user. By terminating the process upon achieving the desired final dryness level, there is no need to re-start the process to finish incomplete drying. In addition, extra energy is not expended to dry the articles beyond the desired dryness level.
Electronic controls have been developed to assist in the operation of such an automatic drying processes. For example, U.S. Pat. No. 3,762,064, to Offut, discloses a system for automatic operation of a dryer in which extra time is added to a drying process according to a predetermined table. A selection of a dryness level beyond a predetermined level (e.g. damp-dry) results in the addition of extra time. The duration of this extra time is dependent upon the length of time required to reach the predetermined dryness level and the desired final dryness level selected by the user. While this system incorporates a moisture sensor for making a drying operation more efficient, this system is nevertheless highly inefficient, because only one threshold dryness level is detected and the final dryness level is never actually measured, as the time to reach that level is only estimated. Therefore, just as in time dry modes, the articles will often be either under-dried and still wet, or over-dried. Even if the system were able to accurately estimate the time required to be added to a single cycle to reach a desired dryness level, the estimation would need to be performed each time the clothes dryer is run. Therefore, the system does not allow the circuitry to xe2x80x9clearnxe2x80x9d about how the clothes dryer is being run to more efficiently operate and give more accurate time readings for completion of a drying cycle.
U.S. Pat. No. 4,477,892, to Cotton, represents an improvement over the system disclosed in the ""064 patent, and includes sensors or electrodes which contact the wet articles to determine the current moisture level contained therein. Through the system of this patent, the current moisture level inside the machine can be measured at a variety of continuous levels. By comparing the number of conductive electrode xe2x80x9chitsxe2x80x9d during a given time period, it is possible to estimate the current degree of dryness. In any event, when a sense dry mode is selected in a conventional clothes dryer, the user is given little, if any, indication that the cycle is coming to an end.
It is also common to utilize a cooldown sequence or procedure at the conclusion of a drying cycle. During this cooldown procedure, cool or non-heated air is passed through the drum of the clothes dryer for a predetermined period of time to more slowly bring articles of clothing down to room temperature and help prevent creasing therein. In the majority of clothes dryers with a cooldown procedure, the cooldown time is either determined by the user or is preset as a static and unchangeable period of time.
As a result, cooldown sequences can be as inefficient as certain drying operations. First, for a user to correctly estimate the amount of time required for a cooldown cycle, he must take into account, (1) temperature of the drying cycle, (2) clothes load, (3) clothes type, and (4) temperature of the cool air being introduced. Hence, accurate estimations are nearly impossible, and the load is often not cooled sufficiently, or is xe2x80x9cover-cooledxe2x80x9d. Even when a preset cooldown duration is utilized, the result is usually the same. Because individuals use their machines differently, i.e. with different typical clothes loads, different typical clothes type mixtures, and have varying cool air inlet temperatures, any preset cooldown duration will, in all likelihood, be inaccurate.
Therefore, there exists the need in the art to provide a control system for a clothes dryer which allows for an adjustable duration setting for both a sensor dry estimation and a cooldown sequence for subsequent uses.
The present invention is particularly directed to a control system for a clothes dryer including a timer and a sensor which measures a drying parameter to calculate how long, with respect to a predetermined time, the clothes dryer needs to be operated to reach a particular condition and to update the predetermined time for subsequent uses. Additionally, a display is included to show the user the amount of time remaining in the current drying cycle, according to the predetermined time.
In a first embodiment, a moisture sensor is included to measure a current moisture level of articles contained within the clothes dryer. Prior to initiating a drying cycle, the user selects a drying temperature and a dryness level. Through a CPU, the control system determines and displays an expected drying cycle time. At certain times in the drying process, the control system checks the actual duration against the expected duration and updates the time remaining displayed. In addition, the expected duration for subsequent cycles is altered. Specifically, during the first few, preferably ten, runs of the clothes dryer, one-half of the difference between the actual run time and the expected run time is respectively added or subtracted from the expected run time value. And, after each later operation, i.e., operations following the first ten, the expected run time is altered by one-quarter of the difference.
By calculating the expected run time, the expected remaining duration can be advantageously displayed to the user. Accordingly, each time the clothes dryer is run, the time required to reach the selected dryness condition is used to update the existing expected time, to more accurately estimate the time remaining. In this manner, average load conditions are xe2x80x9clearnedxe2x80x9d by the clothes dryer.
The xe2x80x9caveragexe2x80x9d load condition is also used to adjust the length of a cooldown sequence at the end of the drying cycle. In the second embodiment, the clothes dryer includes a temperature sensor for measuring the temperature of an exhaust air flow. Specifically, the control system of the invention measures the temperature of the exhaust air flow when the cooldown sequence is complete. If the temperature is equal to or over 100xc2x0 F. (37.8xc2x0 C.), the control system adds one minute to the next cooldown sequence. If, however, the temperature of the exhaust air flow is less than 100xc2x0 F. (37.8xc2x0 C.), one minute is subtracted from the next cooldown sequence.
Additional objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment thereof, when taken in conjunction with the drawings, wherein like reference numerals refer to corresponding parts in the several views.